Geometric profiles of aerofoils, including wings, propeller blades, rotor/turbine blades, stabilizers, and so on, are in general optimized for a design set of conditions or a mission profile, for example high lift, endurance, low drag and so on. Nevertheless, devices such as leading edge slats and/or trailing edge flaps, permit the geometry of the aerofoil to be varied to a limited degree while airborne, and thus enable operation of the aerofoil at other conditions.
However, aircraft that need at times to operate under a wide range of different conditions may incorporate aerofoil geometries that provide adequate performance for the range of conditions, albeit at a performance loss as compared with the optimum performance that may be obtained at any specific set of conditions with an aerofoil geometry designed for such a set of conditions.
By way of general background, a number of inflatable or shape changing devices are known for altering the shape of aerofoils. For example, in U.S. Pat. No. 6,443,394, an airfoil device is provided for attachment to the wing of an aircraft. The airfoil device has a chamber which is inflatable to provide a lift-enhancing airfoil geometry to the wing and other chambers which are inflatable to provide deicing forces to remove ice accumulation on the wing. When installed on the wing, the airfoil device closely conforms to the wing's airfoil geometry (e.g., low camber, sharp leading edge) when the lift-enhancing chamber and the deicing chambers are in a deflated condition. The lift-enhancing chamber can be inflated during take-off and landing to provide a high camber and less sharp airfoil geometry. If ice accumulates on the wing during high speed flight, the deicing chambers can be repeatedly inflated/deflated for ice removal purposes. As another example, in U.S. Pat. No. 7,195,210, an airfoil member is provided including a geometric morphing device. The geometric morphing device has an inflatable member. The inflatable member has an exterior wall and multiple inflated states. Multiple layers are coupled to at least a portion of the exterior wall and control size, shape, and expansion ability of the geometric morphing device. The geometric morphing device is adjustable in size and shape by changing inflated state of the inflatable member. An airfoil member altering system and a method of performing the same are also provided as well as a method of forming the geometric morphing device.
There are also improvements that may be desired to be incorporated to an existing aerofoil design. For example, US2007/0278354, assigned to the present Assignee, and the contents of which are incorporated herein in their entirety, discloses a high lift, two-element, mild stall wing based on a corresponding high lift, two-element, mild stall aerofoils. An aerodynamic feature referred to as a mild stall ramp, or MS-ramp, is provided at the aft portion of the main body of the aerofoil, on the suction surface thereof, while retaining the bluntness of the leading edge of the aerofoil. Gradual development of separated flow on the MS-ramp, combined with continuous lift build-up at the forward portion of the aerofoil produces mild stall characteristics at the extended range of post-stall angles of attack, and combines features of adaptive geometry with stall/post-stall flight capabilities at the level of maximum lift that is inherent to two-element aerofoils.